1. Field of the Invention
The present invention relates to a photoelectric switch, and in particular, to a photoelectric switch suitable when a plurality of photoelectric switches are to be arranged in parallel.
2. Description of the Prior Art
In general, in a photoelectric switch, a light-emitting element is intermittently driven by an output from an oscillation circuit to produce a pulsated light or optical signal, which is then received by a light receiving element, thereby achieving a switching operation. In a case where a plurality of photelectric switches of this kind are arranged in parallel, if the oscilaltion frequencies thereof are identical or similar to each other, there may occur a mutual interference therebetween and hence a wrong operation takes place in some cases. In order to overcome this difficulty, according to the prior art technology, when a light is received as an input before a photoelectric switch projects a light, the light signal is generated at a timing slightly delayed thereafter.
In accordance with a technology to prevent the mutual interference of the conventional photoelectric switches, in a case where a light is received as an input before a photoelectric switch emits a light, only the light emission timing is slightly shifted or delayed. In consequence, the frequencies are not changed, namely, are similar to each other. This means that the method above is not the fundamental countermeasure to completely prevent the interference. Particularly, the conventinal method is less efficient when three or more switches are disposed in parallel.